1. Field of the Invention
The present invention relates to a network system for transferring for example IP data, a network relay apparatus forming one of components of that network system, a network relay monitor apparatus forming another one of components of that network system, and a method of network operation unique to that network system.
2. Description of the Related Art
In recent years, personal computers have spread rapidly through the public. Further, the Internet has taken off, corporate internet protocol (IP) networks (intranets) have grown in size, voice and data have been integrated in the IP (VoIP), and carriers have begun providing IP virtual private network (IP-VPN) services. IP data communications are becoming ever more important.
Further, networks themselves are becoming more sophisticated in function and in performance. E-mail and the World Wide Web (WWW) have spread and applications for reproduction of moving pictures and audio have become popular. Due to this, the total amount of data traffic has rapidly increased. Further, the networks themselves have been increased in speed. Along with this, use of large volume multimedia data has begun to spread.
Under the above circumstances, with network infrastructure being further built up, the data being transferred by IP diversifying and increasing, and further data communications (IP communications) expected to further spread in the future, much has to be considered when thinking of IP data communications as a whole, for example, (i) the drop in network performance due to the intermixture of traffic with different properties, (ii) the efficient use of networks as infrastructure, and (iii) the selection and control of optimal routes (traffic engineering).
This will be explained further. For example, comparing hypertext transfer protocol (http) traffic when referring to the WWW, where the amount of traffic is not that great with sporadic transfer of single strings of data, and multimedia traffic, where once data transfer begins, a large amount of data continues over a certain long period, while the same IP protocol is used for the two types of traffic, properties of the data differ. For example, on the one hand, the http is used for spreadsheets, viewing information, and other main jobs, while on the other hand, considering the case of use of moving pictures, one type of multimedia data, for entertainment etc., despite the importance of the former http traffic, when the former traffic and the latter multimedia traffic are mixed together, the transfer of data by http traffic and the display of and search for web pages end up taking time.
In multimedia communications, however, it is necessary to transmit data packets constantly using a certain bandwidth or else the data cannot be suitably reproduced at the end system. Further, in multimedia communications, sometimes a high quality display is required. In this case, the amount of traffic further increases, so the network has to ensure a sufficient bandwidth, measures have to be taken to avoid congestion, and measures have to be taken to separate transmission routes.
For this purpose, in the past, for example, in corporate networks, the only step taken has been to use simple preferential control functions of routers or other network relay apparatuses. Further, for services provided by carriers or Internet service providers (ISPs), the only step taken has been to connect footholds of contracting users by virtual private network services. Therefore, while the above simple preferential control is being provided, almost nothing is being done, at present, to manage congestion or manage bandwidth in the network.
Looking at management of congestion, in IP communications, congestion control functions currently rely on the slow start algorithm etc. of transmission control protocol (TCP) provided in the end systems rather than the network. Therefore, there is almost no technology for control of congestion or avoidance of congestion in the infrastructure, that is, the network portion.
Further, a look at the above multimedia traffic shows that data is usually transmitted by a user datagram protocol (UDP)/IP. There is no mechanism for control of congestion in the UDP. Therefore, TCP data transmitted under the above slow start algorithm end up being encroached upon by the UDP data in communications bandwidth.
To solve this problem, for example, there is the Resource Reservation Protocol (RSVP) for guaranteeing the bandwidth of multimedia data. What is guaranteed, however, is mainly just continuous data, that is, multimedia data. It is difficult to apply this bandwidth guaranteeing technology to the sporadic TCP data which accounts for most of the traffic on an IP network.
Further, there is also the differentiated service (Diffserv) technology for preferential control of individual packets. Even if this technology is used in a limited network bandwidth, however, the total amount of data which can be communicated naturally ends up being limited to the network bandwidth. Therefore, sometimes the quality of the data communications cannot be sufficiently secured.
Further, if there are other routes not being made much use of for data communications, those routes could be used as bypass routes. In this case, the bandwidth and other resources of the network could be utilized more efficiently. No such technology however has yet been established.
Summarizing the problems to be solved by the invention, various types of traffic, for example, multimedia traffic for audio or moving picture streams etc. and http traffic for transferring data and viewing web pages, is mixed on networks. In this case, the UDP is used for moving picture traffic such as video-on-demand services. Such traffic however consists of streams of packets continuing over a long period of time. Further, with the above http traffic using TCP, the data tends to be burst like and sporadic in nature with respect to time.
Further, in the same way as http traffic, looking at data transfer protocol using TCP, that is, ftp, ftp is continuous. Further, the time over which the continuous data is sustained differs according to the amount of data transferred. If transferring a file by ftp, during the transfer, the network becomes temporarily overloaded. If it is attempted to view a Web page in this overloaded state, the display of the Web page at the end system ends up becoming extremely slow.
Further, looking at the UDP, this UDP is used for large volume data streams such as for video-on-demand services. The UDP differs from the TCP, however. When there is discarded data, lost data, cyclic redundancy check (CRC) error packets, etc., there is no retransmission function for resending the data. Therefore, when such a UDP stream and TCP data conflict, parts of both data naturally are discarded. TCP however has a retransmission function, so when executing a TCP slow start algorithm, the TCP data ends up being robbed of bandwidth by the UDP data. Therefore, the capacity for transfer of TCP data ends up remarkably falling (the TCP slow start algorithm will be explained in more detail at the end referring to FIG. 30, FIG. 31 and FIG. 32).
Further, as explained above, if there are other routes not made much use of for data communications, it may be considered to use these routes as bypass routes. In this case, it becomes possible to make efficient use of the network as a whole. At the present, however, no practical technique has yet been established regarding the use of such bypass routes.
Due to the above, in the future, along with the diversification of traffic, the increase in multimedia data, and the further spread of IP-VPN services provided by carriers, there will be strong demands for development of traffic engineering maintaining qualities of transmission commensurate with the different types of traffic while enabling the transmission of data by the most suitable route at all times so as to ensure the efficient utilization of networks.